Storage tanks for cryogenic liquids typically include “double” and “full” containment storage tanks for cryogenic liquids. It is not uncommon for such storage tanks to have a form of secondary containment. An outer concrete containment wall can provide secondary containment in the event of a leak in the inner tank. The inner tank is typically made of 11.8 m×3.3 m heavy metal plates comprising stainless steel, aluminum, 9% nickel steel, or other materials suitable for low-temperature or cryogenic service. The inner tank is approximately 33 m tall and has a diameter of approximately 88 m.
The inner tank is typically constructed by positioning a pair of heavy metal plates adjacent one another, using a crane, to form a vertical seam therebetween. A plurality of conventional key plates (FIG. 1) are then welded to one or both of the heavy metal plates adjacent the vertical seam to align the heavy metal plates before the vertical seam is welded. In FIG. 1, each key plate 100 is held in place over the vertical seam 102 by a pair of blank nuts. Each blank nut is welded to a respective heavy metal plate 104, 106 adjacent the vertical seam 102. The key plate 100 is placed over the pair of blank nuts and is secured in place by a pair of bull pins 108, 110. Each bull pin 108, 110 is inserted through a respective opening in the key plate 100 and a respective opening in a respective blank nut. Additional bull pins may then be inserted through the key plate 100 to contact and force one of the heavy metal plates 104, 106 into alignment with the other one of the heavy metal plates 104, 106. At least four (4) and up to ten (10) bull pins may be required to align the heavy metal plates. These bull pins may be used in combination to push the vertical seam 102 out, pull the vertical seam 102 in, open the vertical seam 102 and close the vertical seam 102. Once the heavy metal plates 104, 106 are aligned, a plurality of finger bars 112 are welded to the heavy metal plates 104, 106 over the vertical seam 102 to maintain alignment while the vertical seam 102 is tacked. Because the key plate 100 and finger bar 112 must be welded to the heavy metal plates 104, 106 and forcibly removed by breaking the weld, welding equipment, fire protection, hammers and grinding/polishing equipment are required on site. This process takes time and is subject to numerous work hazards related to welding, hammering bull pins, falling bull pins, stray objects, projectiles, metal splinters and pinch points created by the bull pins and key plate 100. In addition, the key plate 100 cannot adjust to multiple radii because it is flat.
Once enough heavy metal plates have been welded together to form a bottom ring of the inner tank, then next ring is constructed by positioning a plurality of shims (FIG. 3) on a top edge of the bottom ring that will separate the next ring. The next ring is typically constructed in the same manner as the bottom ring by positioning a pair of heavy metal plates adjacent one another on top of the plurality of shims to form a vertical seam therebetween and a horizontal seam between the bottom ring and the pair of heavy metal plates in the next ring. In FIG. 3, each shim 300 must be manually held in place on the top edge 302 of the bottom ring 304 with a pin 301 on one side of a heavy metal plate 306 in the bottom ring 304 while another heavy metal plate 308 is lowered on top of the shim 300 to form a horizontal seam between the heavy metal plate 306 and the another heavy metal plate 308 in the next ring. Once the heavy metal plates 306, 308 are in place, a wedge 312 is inserted through an opening in the shim 300 on another side of the heavy metal plates 306, 308 and is hammered down until the shim 300 is secure. A plurality of conventional key plates (FIG. 1) are then used to align the heavy metal plates in the next ring in the same manner described hereinabove. This process continues until each vertical seam in the next ring is welded. The heavy metal plates in the bottom ring 304 are then aligned with the heavy metal plates in the next ring using a plurality of conventional U-Bars (FIG. 2).
In FIG. 2, each U-Bar 200 is welded in place above the horizontal seam 202. A bull pin 204 is inserted through the U-Bar 200 to align the heavy metal plates 306, 308. As the heavy metal plates in the bottom ring 304 are aligned with the heavy metal plates in the next ring, the horizontal seam 202 is welded and each shim 300 is removed by hammering the wedge 312 up to remove it and hammering the shim 300 out. Besides the inefficiencies and hazards associated with using U-Bars, removing each shim is also subject to numerous work hazards related to hammering wedges in and out, falling wedges, stray objects, projectiles, and pinch points created between the shim and the heavy metal plates. Each ring of the inner tank is constructed in the same manner thus described, which is time consuming, hazardous and requires different types of equipment and skilled labor to complete.